Diaries: Into PoliticsAlan ClarkWeidenfeld and Nicholson £20, pp452Buy it at BOL

It is Tuesday, 8 December 1981. Alan Clark has been lunching with Frank Johnson, then, and now again, a parliamentary sketch writer. Johnson seems to be less interested in talking about the Conservative Party than in Clark's views about the Nazis. 'Yes, I told him, I was a Nazi; I really believed it to be the ideal system, and that it was a disaster for the Anglo-Saxon races and for the world that it was extinguished.' Johnson, by Clark's account, gulps and grins and suggests he can't really mean it.

'Oh yes, I told him, I was completely committed to the whole philosophy. The blood and violence was an essential ingredient of its strength, the heroic tradition of cruelty every bit as powerful and a thousand times more ancient than the Judaeo-Christian ethic.' Johnson persists in disbelieving Clark. And what does he confide to his diary? That it was, indeed, a bit of a joke? No. He complains that Johnson and others take 'refuge in the convention that Alan-doesn't-really-mean-it. He-only-says-it-to-shock, etc. Frank said that people simply will not allow the reality that a "toff" could be serious about these views...'

Alan doesn't really mean it. There is the nub of the problem. At some level, he clearly did mean it and this selection of his earlier diaries, running from 1972-1982 when his famous Diaries begins, makes Clark's fascist views very clear. On several occasions, he toys with the idea of defecting to the National Front. Two NF members come to his constituency surgery; he chats to them and muses: 'How good they were, and how brave is the minority, in a once great country who keep alive the tribal essence.'

The NF won't stand against him, he reassures his Tory Plymouth officials 'because they know I'm the nearest thing they're likely to get to an MP'. He frequently compares his personal situation with Hitler's, recording, for instance, in 1976: 'Obsessed with the fall of the Reich. This is 1944, one year left.' He fantasises about being called to lead the country at a moment of collapse.

So what are we to make of it all? Was Alan Clark sinister, despite his brilliant prose talent and his irresistible wit? For those who never knew him, the best clue comes in a passage from 1979, when he is intriguing to become a Tory whip which, he concedes, would be 'second best from the original concept of galloping across the countryside on a white horse, drawn sword in hand, rousing the populace - but I would settle for it'.

Yes, it is Mr Pooter. If he can't be a darkly handsome Nazi leader, he would settle for the Conservative whips' office. In the end, Alan Clark and his diaries are engaging and tolerable because we will not, cannot, grant him the thing he most wants from his audience - we cannot take him seriously.

This is Pooter with a castle, a collection of cars straight from Toad's garage, a ferocious sexual urge and a deep strain of hypochondria. We laugh with him, some of the time, but more often we laugh at him. He came to realise it, which must have been almost intolerable. For all the swagger and swish, the style and the curled lip, he was a comic figure and knew it.

The comedy, as with other comic diarists, depends heavily on the repetition of key themes. He is constantly giving up backgammon and just as constantly, a few days later, losing yet more money at it. He is always on the sexual prowl, generally unsuccessfully, and finds the oddest things provoke his turbulent libido.

To my eye, one of the least explicable, funniest moments comes during an assessment of his bodily decay ('eyes puffy' etc): 'A bit stiff, can get quite unpleasant twinges from shoulder if, eg, turning round while holding up phone.' And then, apropos of nothing: 'Being 51 makes me feel quite lecherous.' What? Run that past us again?

Similarly, below the show-off remarks, his politics are simply incoherent. He is pro-Nazi but also proud of the 'Spitfire summer'. He is violently anti-European but entranced by that original Europeanist, Harold Macmillan. He is utterly committed to Margaret Thatcher and the Tory right wing except when he is buttering up her sworn Cabinet enemy and leading 'wet', Francis Pym, telling him he'll be Prime Minister in two years if he resigns and takes her on. Does this seem just a little odd, even to him? It does.

'What a rich, endlessly varied and exciting world politics is for those who are addicted to it,' he gushes. 'And how inextricably woven are the different strands of greed, ambition, cowardice and idealism. No one's motives are pure; certainly not mine.' Yes, it's that man again - Mr Pooter goes to Parliament.

Perhaps it is impossible to be a great diarist without being enough of a fool to play Everyman at his weakest moments as well as at the tender ones. Clark's desperate lechery, repeatedly broken promises to himself to reform, his snobbery, his political inanities, his low moments of self-rebuke and even his hypochondria are all very reminiscent of that great diarist, James Boswell and, at times, of Samuel Pepys himself. The diaries of the high-minded and consistent cannot be nearly as amusing.

This volume is duller than the first, later one, simply because less happens to Clark during it; he is not so central to political life and has less to reveal. Debts, health, his lack of real political success and his gloom about his children and properties produce a whining note at times which grates. The high comedy is here - his buying-off of a former mistress with the help of Jonathan Aitken and a briefcase with a bugging device is one for the anthologies - but it is less rich than the previous volume.

Alan Clark wanted to make the world gasp and tremble. In the end, he made it gasp and giggle instead. The answer to the 'Nazi question' was less that Alan-didn't-really-believe-it, more that no-one-really-believed-in-him.

That, I suspect, was a source of real private pain, too private, even, to be recorded in his diaries. Good news for the rest of us, though.